1. Field of the Invention
The present invention relates to a displacement information detection apparatus and, more particularly, to an apparatus suitable for optical displacement sensors such as an encoder, a speed sensor, an acceleration sensor, and the like, which measure a displacement and a speed of an object by utilizing the fact that when a light beam radiated onto an object being displaced is diffracted or scattered, the diffracted or scattered light beam is phase-modulated according to the displacement or the moving speed of the object.
2. Related Background Art
Conventionally, optical displacement sensors, e.g., an optical encoder, a laser Doppler speedometer, a laser interferometer, and the like, for obtaining a physical quantity such as movement or displacement of an object with high precision by radiating light onto the object are widely used mainly in the fields of NC working machines, OA equipment, robots, and the like. As a conventional displacement sensor, for example, Japanese Laid-Open Utility Model Application No. 1-180615 and Japanese Laid-Open Patent Application No. 62-121314 disclose optical encoders. Also, Japanese Laid-Open Patent Application No. 2-262064 discloses a laser Doppler speedometer.
In consideration of an application of the displacement sensor to wider fields, the displacement sensor is required to have a more compact structure (on the order of mm), and higher precision and resolution (on the order of 0.1 .mu.m). If the displacement sensor has a size on the order of mm, it may be used while being directly adhered to an object to be measured by, e.g., an adhesive. For this reason, the displacement sensor can be used for smaller devices, and the application field range can be remarkably widened. However, it is difficult for the conventional displacement sensor to achieve both a compact structure and high-precision/high-resolution characteristics.